Greeks,Rus,Lombards,Saxons,Persians,Arabians,Germans,Mongols,Huns,Turks, these, and many more people made up the Byzantine Empire. Most of these people were refugees or immigrates from failing Kingdoms or just seeking a better life in Byzantium. The Empire asked service from them in exchange for fertile land and citizenship. You see, the Byzantines did not ask them to change their traditions, faith, or beliefs, this made Byzantium a immigration magnet. The Byzantines eventually converted them, but not forcefully. The difficulty of uniting so many cultures seems impossible, but yet the Byzantines united them into an Empire.

If I remember the database article about the Ottoman Empire they did the same thing. It's not possible to rule over an empire of that size if everyone is forced to change their traditions, costumes, beliefs, etc. anyways that's based on AC again and I really hope that I am even partly right:) (please tell me if I'm right or wrong)

Well, the person mostly responsible for letting the Byzantines keep their ways was Mehmed II, but not out of kindness, he knew as long as the Byzantine people survived the world would remember his conquest. Maybe the Ottoman Empire was more merciful then I thought, however they turned a blind eye whenever Turks bothered the Byzantines.